I'm very new to REW, but I've taken quite a few measurements and have messed with placement and crossover with my dual PSA XS15s and think I've finally got about the best response I can before EQ or room treatments.

I'm very new to REW, but I've taken quite a few measurements and have messed with placement and crossover with my dual PSA XS15s and think I've finally got about the best response I can before EQ or room treatments.

Does this look like a pretty good response, or am I just lost?

Well, you're +/- ~10 dB, from 10 to 100 Hz, so that's pretty typical of a lot of rooms. Is this just the subs, or subs and speakers? If the later, what crossover setting are you using?

Craig

Lombardi said it:Perfection is not attainable, but if we chase perfection we can catch excellence."

Cool! What do I do next? Treatment, EQ, nothing and just enjoy??
This is subs+mains, 80hz.

Here's the waterfall:

I think that wicked thing at 60hz is my fridge.

Acoustic treatments, i.e., bass traps, can help from about 100 Hz up, depending on how thick they are. However, below 100 Hz, in order to be effective they need to be large and unwieldy. Resonator style absorbers can target specific frequencies, but they require some specialized design and construction skills. Your best bet will be some form of EQ. With all the extra decay time in the LF's in your room, something like Audyssey XT32 or the AntiMode 2.0 would be beneficial.

Turn your fridge off when you're taking measurements.

Craig

Lombardi said it:Perfection is not attainable, but if we chase perfection we can catch excellence."

Acoustic treatments, i.e., bass traps, can help from about 100 Hz up, depending on how thick they are. However, below 100 Hz, in order to be effective they need to be large and unwieldy. Resonator style absorbers can target specific frequencies, but they require some specialized design and construction skills. Your best bet will be some form of EQ. With all the extra decay time in the LF's in your room, something like Audyssey XT32 or the AntiMode 2.0 would be beneficial.

Turn your fridge off when you're taking measurements.

Craig

This is with Audyssey XT:

Would you recommend XT32 or Antimode over manual EQ ala the BFD? The BFD was probably gonna be my next step.

Would you recommend XT32 or Antimode over manual EQ ala the BFD? The BFD was probably gonna be my next step.

Audyssey helped a fair amount. XT32 would help even more, but it would be a lot more expensive than a BFD. Lots of folks get good results with the BFD, and REW makes EQ suggestions for use with it. I would say give it a shot.

Craig

PS. Do you have the accompanying FR graph?

Lombardi said it:Perfection is not attainable, but if we chase perfection we can catch excellence."

Audyssey helped a fair amount. XT32 would help even more, but it would be a lot more expensive than a BFD. Lots of folks get good results with the BFD, and REW makes EQ suggestions for use with it. I would say give it a shot.

Are you taking the measurement at aloud enough volume? Your fridge shouldn't affect the FR graph and as Dominguez says that low frequency tale is all wrong since you say no EQ was applied there. Your measurement needs to be captured at an spl above the noise floor in the room.

Are you taking the measurement at aloud enough volume? Your fridge shouldn't affect the FR graph and as Dominguez says that low frequency tale is all wrong since you say no EQ was applied there. Your measurement needs to be captured at an spl above the noise floor in the room.

Below 30Hz that noise floor can be quite high. If you're anywhere near a road it's not unusual to get a reading in excess of 70dB below 20Hz with the system off. Your mic is picking up road noise conducted through the ground, from even a mile off. The gear can 'hear' it, but at those levels you can't.
When I took RTAs at major concerts the levels below 30Hz were a constant, whether the band was playing or not. The source of the below 30Hz content was traffic, both vehicular and foot, and all the various refrigeration units scattered about the venue.

Yup, I've read that whole thread, thanks! The 2496 is the one I'll get then...but, about that response below 20hz - that may be an anomaly, see below.

Quote:

Originally Posted by dominguez1

You're rising response from 15hz to 10hz looks unusual. What mic are you using with REW? Radio Shack SPL meter with the correction file? I'm guessing this is the case based on that rising response...

You called it - I am using a Rat Shack SPL meter (w/correction file). Guess I need to invest in a real mic, eh? I'm also using my on-board sound card in my PC, not a good idea either from what I've read. I'm gonna need to get the right equipment before I can get reliable measurements I guess. What's the recommended (internal) sound card?

Quote:

Originally Posted by Archaea

Are you taking the measurement at aloud enough volume? Your fridge shouldn't affect the FR graph and as Dominguez says that low frequency tale is all wrong since you say no EQ was applied there. Your measurement needs to be captured at an spl above the noise floor in the room.

Turn the volume up 15dB and measure again.

That may or may not be my fridge, I've yet to take a measurement with the AVR off to track down any noises, but will soon. I was taking measurments at -5db on my AVR so I could turn it up a bit more.

Quote:

Originally Posted by Bill Fitzmaurice

Below 30Hz that noise floor can be quite high. If you're anywhere near a road it's not unusual to get a reading in excess of 70dB below 20Hz with the system off. Your mic is picking up road noise conducted through the ground, from even a mile off. The gear can 'hear' it, but at those levels you can't.
When I took RTAs at major concerts the levels below 30Hz were a constant, whether the band was playing or not. The source of the below 30Hz content was traffic, both vehicular and foot, and all the various refrigeration units scattered about the venue.

Yup, I've got a major thoroughfare about 2 blocks from my house, but there are two rows of houses in between. Not much I can do about that I guess.

I don’t have any experience with the XS15s but seriously doubt they’ll play as low as reflected on those graphs.

I first used REW with a radioshack spl meter (and calibration file) and then later upgraded to a CSL calibrated Dayton mic. The responses measured very similar from maybe 20-30hz up to, say, 12khz. But the radioshack meter overstated the lowest frequencies. I think that’s part of what you’re seeing.

Also, my laptop’s soundcard provided a different response than when using my Behringer 202 and 302 so I imagine that could be causing you issues too.

I think you’re right about the 60hz issue being the fridge; I’ve gotten a similar result when forgetting to unplug my minifridge. Also, I used to have an AC unit nearby and that could show up on my results too if running; I usually temporarily turn off the heat/ac to avoid any related noise from indoors/out.

One more thought - your first graph looks similar to what I’ve gotten when I’ve accidentally had Audyssey’s Dynamic EQ enabled. That boosts the low end and could explain why you’re 10db higher from 20-40hz than 40-80hz. Not sure you can even use DEQ without Audyssey enabled – and looks like your graph after running Audyssey flattened everything out – so probably not what’s going on but figured I’d throw that out there.

My guess – you’re actually rolling off around 25hz and not getting much of anything past 17-18hz. If you’re flexible with placement options, I’d play around with that…but assuming your green graph is mostly accurate, that looks pretty good. A BFD could trim/boost a few places but not sure you’ll hear much of a difference.

I've found out in another thread that the problem at 60hz is most likely being caused by a ground loop hum produced by my PC that I'll have to try to correct - or, use a laptop running off battery power (I don't currently own one).

Quote:

Originally Posted by benunc

I don’t have any experience with the XS15s but seriously doubt they’ll play as low as reflected on those graphs.

I first used REW with a radioshack spl meter (and calibration file) and then later upgraded to a CSL calibrated Dayton mic. The responses measured very similar from maybe 20-30hz up to, say, 12khz. But the radioshack meter overstated the lowest frequencies. I think that’s part of what you’re seeing.

Also, my laptop’s soundcard provided a different response than when using my Behringer 202 and 302 so I imagine that could be causing you issues too.

I think you’re right about the 60hz issue being the fridge; I’ve gotten a similar result when forgetting to unplug my minifridge. Also, I used to have an AC unit nearby and that could show up on my results too if running; I usually temporarily turn off the heat/ac to avoid any related noise from indoors/out.

One more thought - your first graph looks similar to what I’ve gotten when I’ve accidentally had Audyssey’s Dynamic EQ enabled. That boosts the low end and could explain why you’re 10db higher from 20-40hz than 40-80hz. Not sure you can even use DEQ without Audyssey enabled – and looks like your graph after running Audyssey flattened everything out – so probably not what’s going on but figured I’d throw that out there.

My guess – you’re actually rolling off around 25hz and not getting much of anything past 17-18hz. If you’re flexible with placement options, I’d play around with that…but assuming your green graph is mostly accurate, that looks pretty good. A BFD could trim/boost a few places but not sure you’ll hear much of a difference.

I just ordered one of them new-fangled CSL calibrated USB mics, so I should be able to get some better measurements soon!

Dyn EQ (and Audyssey) were most definitely turned off.

I'm gonna wait on doing anything else until I get the new mic and resolve my hum issue so I can see what's really going on.

Been reading up on REW all day (slow day at work) and have learned a lot (waterfalls, ETC, etc.) but it sure is intimidating at first!

I've found out in another thread that the problem at 60hz is most likely being caused by a ground loop hum produced by my PC that I'll have to try to correct - or, use a laptop running off battery power (I don't currently own one).
I just ordered one of them new-fangled CSL calibrated USB mics, so I should be able to get some better measurements soon!

I think I found the culprit - it was my (decidedly old & cheap) 50' RCA cable I was using to feed audio from my PC to my AVR. I don't have any others long enough to reach (35') so just ordered a new one from Monoprice. Hopefully this will fix that hum.

Sounds like you have a ground loop thing going on between the circuit breaker your PC is plugged into and the circuit breaker your AVR is plugged into.

One way to check this is to electrically gang an extension cord off the outlet your AVR is plugged into and run a extension cord to your PC. I suffer from the same experience you're having in that anytime I hook the PC audio out (headphone out) to the AVR's AUX in, I get an instantaneous ground loop situation. That's just the way of ground loops as pretty much anything can be responsible for causing a ground loop to develop.

When running sweeps, if necessary, eliminate any additional ground connections to the computer; router, et cetera. Maybe after jumpering the power from the aVR outlet to your PC, you'll need to run a grounding cable from the PC's case to the AVR's case so as to establish a common ground.

Thanks BeeMan, I'll try that this weekend. Maybe I just wasted a few bucks on a new cable.

Rather then my seeing it as a waste, I like to see it as adding to or upgrading my collection of interconnect cables and other basic but necessary who-ha. Would you like to take a look at my big cable box that's filled with every imaginable, but much needed interconnects from days gone by?

My latest add was a "better" sound meter that has a lower measuring floor (40dB) with an auxiliary calibrator. Now I have two calibrated sound meters that I can depend on to tell me how forever messed up and hopeless my settings are.

(currently taking a short two week long break from measuring the room and dealing with all the rest)

Do you have flexibility with sub placement? Flatten the response with placement as best you can, EQ is the last tool in the tool bag.

IMHO you can forget meaningful output to 10Hz from 1000w and two sealed 15s unless your room is like 4'x4'. The 10Hz plot is a measurement error, noise floor, or other meausrement artifact. Either way as you turn it up you will see that 10Hz doesn't hold up to the resf of the FR unless your ambient is that high.

Here is a plot someone measured over on HTS on those subs

Unless you have a nasty peak between 10-20Hz, EQ below 20 for those subs is pretty useless IMO. You don't have enough headroom to boost so all you could do is shave a peak if there is one but those subs don't put out much below 20 to begin with......

Alan P, based on the graph posted in the OP, I'd check your sub distance settings in the AVR menu. In our case, Audyssey reports 26' when they're a measurement tape reading of 13' and 12 respectively. The main listening position is a bit asymmetrical because the main listening position is a bit skewed to one side of the center line. Changing the distance setting to 13' made a world of positive difference. I haven't measured the difference as I'm taking a two week sabbatical from room measurements but simply changing the distance to the measured distance made a hugely and very noticeable, positive change. When I come out of my self-imposed sabbatical, I'll measure the room and graph the change that was made.

The rule of thumb I've read, there's a listening room reading vs a tape measure room reading. Measure and set your sub distances according to what the tape measure tells you and if an improvement, you're good as the distance setting is not a set in stone type of setting. And if things seem worse, go with the Audyssey recommendation.

As to placement of the subs, if you haven't found out already, one will be surprised how much moving a sub a few feet, to the left or right, backwards or forward a foot or two will make in overall subwoofer performance. I also use all three controls to make parametric changes; volume, phase and frequency. And to be encouraging, in my opinion, nothing is sacred (set in stone) regarding subwoofer settings and placement. It's all about what works. I also find one has to do the best they can regarding subwoofer placement based on WAF, room placement, furniture arrangement and reflective surfaces that one can't do anything about (oh hell no, I'm not filling my room with acoustical panels) as there's the ideal and there's the reality of the issues.

As a suggestion, remove all EQ'g efforts, set your sub the best one can regarding parametric settings and sub placement, then bring in EQ'g efforts.

Do you have flexibility with sub placement? Flatten the response with placement as best you can, EQ is the last tool in the tool bag.

IMHO you can forget meaningful output to 10Hz from 1000w and two sealed 15s unless your room is like 4'x4'. The 10Hz plot is a measurement error, noise floor, or other meausrement artifact. Either way as you turn it up you will see that 10Hz doesn't hold up to the resf of the FR unless your ambient is that high.

Yeah, after doing a lot of reading up on REW, I've found that I did my measurements all wrong - SPL meter, to low of output (75db), and that nasty ground loop - all probably contributing to throwing my measurements way off.

I'm gonna wait until I get my new calibrated mic, figure out the ground loop and only then do some real measuring!

I do have flexibility with sub placement, and have been experimenting. But, now that I know I can't trust my measurements, I'll have to start all over when I know I can trust them. No big deal, it's all part of the fun of this hobby, right?

Here's a pic of my room, but I have since moved the front left sub to the back left corner of the room (also change phase to 90 degrees) and got better response with REW (graph in first post - but, again, can't be trusted yet):

The 60hz issue very well might be due to a ground loop. If so, you should know - you'll hear the buzzing coming from the subs. I've got a ground loop issue but it only presents itself when using my BFD or when taking measurements with my laptop's AC cord plugged into the wall (my solution was to buy a Hum-X device for my BFD and use my laptop's battery when taking measurements). A ground loop won't throw the entire measurement off - it's just a narrow impact right at 60hz; the rest of the response is unaffected.

If you include the mic and sound card lines on the graphs, they might reveal issues with your set-up.

Looks like a very large room - unfortunately, you're definitely not getting near 10hz in there.

Once you get accurate measurements, it's easy to start experimenting with different positioning, phase, etc to get the best response. Once you have the best response you can get pre-EQ, run Audyssey, then depending on that response, determine if you could benefit from further EQ from a BFD/minidsp. I'd have gone with the minidsp had it been around when I bought my BFD (if it was, I hadn't heard of it).

The 60hz issue very well might be due to a ground loop. If so, you should know - you'll hear the buzzing coming from the subs.

I also heard it coming from the mains. By pulling the AVR connection to the mains, problem fixed.

By turning the room analyzer on to the provided Real Time Analyzer (RTA), with nothing running but background noise, will expose naturally occurring standing waves. I have a half dozen naturally occurring standing waves that are not audio related. One is at 60Hz and two more are at the 60Hz harmonic of 120Hz and 300Hz. For whatever reason, I don't see a 240Hz harmonic. I only care out to 120Hz.

Either which way, the 60Hz buzz and it's corresponding harmonics are not consequential to the problem (too focused or narrow of bandwidth) caused by Audyssey's recommendation of setting the subwoofer distance at twice the measured distance to the subs. Sometimes, one had to play God and overrule Audyssey's provided recommendations to the AVR.